<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>背景色透明写法</title>
    <style>
      div {
        width: 300px;
        height: 300px;
        /* background-color: black; */
        /* background: rgba(0, 0, 0, 0.3); */
        background: rgba(0, 0, 0, .3);
      }
    </style>
  </head>

  <body>
    <div>隐形的翅膀</div>
  </body>
</html>
